In situ synchrotron radiation photoelectron spectroscopy study of the oxidation of the Ge(100)-2 × 1 surface by supersonic molecular oxygen beams

Abstract

In situ synchrotron radiation photoelectron spectroscopy was performed during the oxidation of the Ge(100)-2 × 1 surface induced by a molecular oxygen beam with various incident energies up to 2.2 eV from the initial to saturation coverage of surface oxides. The saturation coverage of oxygen on the clean Ge(100) surface was much lower than one monolayer and the oxidation state of Ge was +2 at most. This indicates that the Ge(100) surface is so inert toward oxidation that complete oxidation cannot be achieved with only pure oxygen (O2) gas, which is in strong contrast to Si surfaces. Two types of dissociative adsorption, trapping-mediated and direct dissociation, were confirmed by oxygen uptake measurements depending on the incident energy of O2. The direct adsorption process can be activated by increasing the translational energy, resulting in an increased population of Ge2+ and a higher final oxygen coverage. We demonstrated that hyperthermal O2 beams remarkably promote the room-temperature oxidation with novel atomic configurations of oxides at the Ge(100) surface. Our findings will contribute to the fundamental understanding of oxygen adsorption processes at 300 K from the initial stages to saturated oxidation.

Microscopic Views of Atomic and Molecular Oxygen Bonding with epi Ge(001)-2 × 1 Studied by High-Resolution Synchrotron Radiation Photoemission

“…Nevertheless, the investigation of a thick Ge oxide film does not help us to fully understand the oxygen-contacted Ge-Ge dimers layer. Another method, an in vacuo process using supersonic molecular oxygen beams, only produces the 1+ and 2+ oxidation states in the sub-monolayer thickness [31]. The weak bonding of molecules on Ge(001) [32,33] and the confined adsorption site at the surface dimers without any insertion into the Ge backbonds [34] have rendered the four charge states unlikely to be formed at the interfacial region of Ge(001).…”

Thermally Activated Reactions of Phenol at the Ge(100)-2 × 1 Surface

“…Also, although structures with further subsurface migration of O were attempted by DFT calculations, no structure with additional stability compared to the state V could be located, possibly due to the low reactivity of the Ge substrate toward oxidation. 31,32…”

“…Therefore, it can be understood that new bonds are formed along with the breakage of similarly stable bonds, and thus the magnitude of the overall energy change accompanying thermal reaction of phenoxy/Ge(100) is small. Also, although structures with further subsurface migration of O were attempted by DFT calculations, no structure with additional stability compared to the state V could be located, possibly due to the low reactivity of the Ge substrate toward oxidation. , …”

Dynamic Observation and Theoretical Analysis of Initial O2 Molecule Adsorption on Polar and m-Plane Surfaces of GaN

“…An O 2 molecule beam, in which all of the molecules have the same energy, is suitable for fundamental studies of the O 2 dissociative oxidation. Yoshigoe et al developed a real-time XPS apparatus that can detect photoelectrons generated from the sample irradiated by the O 2 molecule beam to investigate the initial surface oxidation process on Si and Ge. , …”

“…Yoshigoe XPS apparatus that can detect photoelectrons generated from the sample irradiated by the O 2 molecule beam to investigate the initial surface oxidation process on Si and Ge. 23,24 In this study, we applied the same technique to observe the surface oxidation of GaN. The O 1s core XPS spectra were continuously observed in real time during irradiation of the O 2 molecule beam on (0001) (Ga-polarity (+c)) and (0001̅ ) (Npolarity (−c)) and m-plane (101̅ 0) surfaces of GaN to monitor the oxidation process on each surface.…”